Just after 6 p.m. firefighters went to the lower Grafton Street area and encountered extremely high readings for natural gas in the area, District Chief Frank DiLiddo said.

Typically, firefighters wait for utility crews from NStar to arrive, but because of the high levels of gas detected in the area, they started opening up manhole covers to vent the gas. The chief said venting the manholes can help prevent the gas from traveling horizontally into nearby basements.

NStar crews arrived and eventually narrowed down the area of the leak to Houghton Street. The distinctive odor, added to the normally odorless gas to make leaks more noticeable, was obvious on Houghton Street.

Firefighters forced entry into a building to determine if gas had reached the basement. Checks of several other area homes revealed the leak was contained to the street, Chief DiLiddo said.

The hilly, snowbank-narrowed neighborhood became a traffic nightmare, as traffic spilled onto side streets barely able to handle two-way traffic. Police officers and firetrucks blocked as many streets as possible.

Chief DiLiddo said he understood the inconvenience caused by shutting down one of the city's busiest arteries — Grafton Street was shut down from around Walgreens up to the Hamilton Street rotary — but said it was for everyone's safety.

“With such a high concentration of gas, we wanted to minimize any type of ignition sources,” Chief DiLiddo said.

Around 7:30 p.m., several more NStar crews arrived, and several firefighters started to pack up. Around 7:45 p.m., the road was reopened, and NStar crews were preparing to dig up Houghton Street to pinpoint the leak, Chief DiLiddo said.